阅读理解。 Every day after school millions of children-most of them in middle school or high school-head home to empty houses. Often, they're on their own until dinnertime or later-not by choice, but by necessity. While they may be old enough to avoid setting the house on fire, each afternoon is still a minefield (充满隐伏危险 的事物). It's a minefield hidden with drugs and alcohol, Internet addiction, violent video games and,perhaps worst of all, loneliness. But families have little choice. With more parents working full-time than ever before, it's no surprise that the number of so-called latchkey kids in the United States is also at an all-time (空前的, 创纪录的) high. Up to 15 million of the country's 49 million school-age children spend part of the workweek on their own; almost a third do so at least three days a week. The afternoon hours are also dangerous when it comes to crime. The U.S. Department of Justice reports that the rate of violent crimes reaches its highest point between 3 p.m. and 4 p.m.-nearly the same time at which children are most likely to be victims of such crimes. One study found that those who are on their own 11 hours or more a week are twice as likely as those who aren't to drink or smoke. All this leads some health experts to an important conclusion. 'Lack of adult involvement is one of the strongest influences on bad behavior,' says Robert Blum,chairman of population and family health at Johns Hopkins School of Public Health in Baltimore. In fact, he and others believe it's stronger than background, family income, or family structure. 'And the more time teens spend unsupervised (无人监督的), the worse they'll behave.' Blum and others believe teachers can help by transforming their schools into more nurturing environments. He also argues for more and better after-school programs. But the final responsibility lies with parents. One survey found that almost 90％of students agree that, 'Even though I might complain about it, sometimes I need to be pushed by my parents to do things that are good for me.' 1. The passage is written to _____. A. teach parents how to have good relationship with their kids B. warn teenagers to stay away from drugs and alcohol C. remind parents to pay more attention to teenagers who spend time alone at home D. express the hope that kids should spend more time studying after school 2. The underlined words 'latchkey kids' in paragraph 3 probably mean _____. A. children who are at home alone after school B. children who are addicted to video games C. children who are in charge of the house key D. children who spend more time online than at school 3. What is the main reason for bad behavior in children, according to the passage? A. Violence B. Lack of supervision C. The Internet addiction D. Drugs 4. Which of the following is NOT a good way to prevent children from behaving badly? A. Having children spend more time with adults. B. Having more and better after-school programs. C. Having more supervision from parents. D. Having children chat more with their friends.